Monthly Archives: November 2016

Waspmote Plug & Sense! : Solar-Powered Wireless Sensor Platforms

Today, we use sensors for a myriad of activities such as intrusion detection, fall detection, patient surveillance, art and goods preservation, offspring care, animal tracking, selective irrigation, and many more. Where the sensor network has to operate outdoors, what can be a better way of powering them other than through solar means?

Using an external or internal solar panel, one can safely recharge batteries for the system. For external solar panels, the panel is usually mounted on a holder tilted at a suitable angle ensuring the maximum performance of the outdoor installation. When space is a major challenge, such as indoors, the solar panel can be embedded on the front of the enclosure. Typical rechargeable batteries used for powering loads are rated 6600mAh, and this ensures the sensors do not stop working even when the sun is not providing adequate light.

Such platforms of wireless sensor networks provide solutions for Smart Cities. Waspmote Plug & Sense! from Libelium is a system of encapsulated wireless sensor devices that allow system integrators to implement modular wireless sensor networks in a scalable manner. The Libelium system reduces the installation from days to just hours.

Each node of a Waspmote Plug & Sense! comes with six connectors. You can connect sensor probes to these connectors directly and the system is ready to install and easy to deploy. Using connectors ensures that the services remain scalable and sustainable. The possibility of powering the platform through solar power allows energy harvesting and years of autonomy.

Once the sensors have been installed, the nodes on the Waspmote Plug & Sense! can be programmed wirelessly. This is possible because of the special feature, OTAP or Over The Air Programming, incorporated into the platform. Thanks to OTAP, users can replace or add sensors without having to uninstall any of the nodes. This helps to keep the maintenance levels within reasonable limits. For example, to extend the service, you can easily add a noise sensor to a network consisting of CO2 probes, simply by attaching it.

The applications are endless for the Waspmote Plug & Sense! platforms. Apart from Smart Cities, the models are preconfigured for creating other widely applicable services out of the box, such as radiation control, ambient control, smart security, air quality, smart agriculture, smart parking and so many more.

You can use these sensor platforms anywhere in the world, as they use the generally available radio frequencies 2.4GHz and 868/900MHz, besides complying with certification standards such as CE, FCC, and IC. Usually, these sensor platforms send information to a sensor gateway that in turn, uploads the data to a cloud service. Therefore, the data is accessible from anywhere in the world and users can integrate it easily into third-party applications.

Use of solar-powered wireless sensor networks makes it so easy for adding a new sensor that municipalities find they do not have to reinstall the network for Smart Cities. The solution reduces the complexity of the installation and its maintenance, while providing it with a high degree of scalability. Available with IP65 enclosures for outdoor deployment and no software license fees, these platforms offer remarkable opportunities.

Connecting To a Raspberry Pi via an Ethernet Cable

You can use your Raspberry Pi or RBPi single board computer in different ways. Sometimes you may have a keyboard, mouse, and display to connect to your RBPi to use it as a regular computer. At other times, you may prefer to communicate with it through another computer such as a desktop or a laptop. Your method of communication may also vary. For example, if your RBPi is at a distance, you may have to connect to it over the Internet via Wi-Fi.

However, Wi-Fi may be an unreliable and a slow way of connecting to your RBPi if you are communicating with it often using SSH or a remote desktop application. Rather, a faster method would be to use a direct Ethernet connection, which would also be a lot more stable. Since you are connecting to your RBPi directly with an Ethernet cable, you are actually bypassing your local network and not sharing the bandwidth with other computers. Moreover, a direct Ethernet connection allows you to connect to your RBPi even when you are away from your home network, experiencing slow connectivity and or network time outs.

For this, all you need is an Ethernet cable. You will need to assign a static IP address to the Ethernet port of the RBPi. The static IP address will depend on the IP address of the computer and its Ethernet adapter that you will be using to connect to the RBPi. The process of assigning a static IP address is straightforward and should be easy for any OS.

If you are using a Windows computer to connect to your RBPi, open up the Network Connections window from the task bar or by accessing the Control Panel. Now look at the Properties of the Ethernet connection under Internet Protocol Version 4. This will show an IP address of the form 10.0.0.6 or similar.

In some cases, the internet connection may also be set for automatic assignment. Here, you need to connect your RBPi to the computer via an Ethernet cable first. Now access the Windows command prompt and use the ipconfig command to see the address your computer has automatically assigned to the connected RBPi. Next, you will also need to note the default gateway IP, which is the local IP address of your network router.

Apart from the above, you will also need to find out the IP addresses of the domain name servers used by your RBPi for finding websites on the Internet. This you can find out by executing the command cat /etc/resolv.conf on the command prompt of your RBPi.

Now you must edit the /etc/dhcpcd.conf file on your RBPi and modify the three IP addresses in the file. Change the last number of the IP address of your computer’s Ethernet adapter, to any other number between 0 and 255. This becomes the static IP address you will use to SSH or connect remotely to your RBPi.

The static router is the IP address of the default gateway IP you noted earlier and the static domain name servers are the IPs you noted from the /etc/resolv.conf. Save the dhcpcd.conf file and reboot your RBPi. Enjoy your connection.

Different Types of Light Sensors

Light falling on to the surface of a light sensor generates an electrical output proportional to the strength of the incident illumination. The sensor responds to a band of radiant energy existing within a narrow range of frequencies in the electromagnetic spectrum, which we characterize as light. These frequencies range from the infrared to the visible and continue to the ultraviolet region of the spectrum.

Most light sensors are passive devices for converting the light energy of the spectrum into electrical signal. Light sensors are also known as photo sensors or photoelectric devices, since they convert photons into electrons. We can group photoelectric devices into two main categories. One generates electricity when illuminated – such as photovoltaic or photo-emissive, etc. and the other changes their electrical properties in some way – such as photo-resistors or photo-conductors, etc. Accordingly, the following classification emerges.

Photo-emissive cells

These are formed from light sensitive material such as cesium. When struck by a photon of sufficient energy, the light sensitive material releases free electrons. As high frequency light contains photons of higher energy, they have a better chance of producing more electrical energy.

Photo-conductive cells

The electrical resistance of these cells varies when subjected to light. They are made of semiconductor material and the light hitting it causes photoconductivity, which controls the current flow through the material. Cadmium Sulphide is the most common material for making photo-conductive cells, such as the light dependent resistor or LDR.

Photo-voltaic cells

These generate an EMF or electromotive force proportional to the radiant light energy falling. Although similar in effect to the photo-emissive cells, these are made up of two semiconductor materials sandwiched together. Solar cells are the most common photovoltaic cells in existence.

Photo-junction devices

These photo-devices are made of true semiconductor devices such as PN-junctions that use light for controlling the flow of electrons and holes. Specifically designed for light penetration and detection applications, their spectral responses are tuned to the wavelength of light expected to be incident on the device.

Applications of light sensors

LDR photocell: The Cadmium Sulphide photo-resistive cell is the most common example of this device. The resistance of these cells when not illuminated is of the order of 10M ohms, which reduces to the level of 100 ohms when fully lit or illuminated. As the voltage drop across a resistor increases with its resistance value, an LDR photocell can generate different voltages in a potential divider circuit based on the amount of light falling on it.

Light activated switch: This is basically a dark sensing circuit, with a light sensor in series with a potentiometer forming one arm of a simple resistance bridge network and two fixed resistors forming the other side of the bridge. By changing the potentiometer, one can balance the bridge when the light sensor is illuminated, for example by sunlight. The absence of sunlight causes the bridge to unbalance and the resulting potential difference is amplified by an operational amplifier to operate a relay or a switch.

Today, it is common to find cameras that do not operate with a film, but with charge coupled devices that convert the light falling on them to an electronic image.

MEMS Technology Helps To Measure Flow

Smart technologies are creating compact and lightweight sensing elements. Apart from being optimal, fast, and efficient solutions, these are not limited to only the data input functions as the conventional sensing technologies are. Rather, they integrate the areas of sensing and control while offering high-value information that humans or systems can subsequently process. Several unique and advanced technologies such as MEMS form the concept of sensing and control expertise. For example, flow sensors use the ButterflyMEMS technology to operate.

Flow sensors using the MEMS technology operate with major advantages. For example, they can easily measure flow speed ranging from 1 mm per second to 40 m per second. To understand this better, ButterflyMEMS technology can sense the fluttering of the wings of a butterfly and the roar of a typhoon with equal ease. A tiny MEMS flow sensor does all the work and it is the size of a 1.5 mm square chip, which is only 0.4 mm thick.

Conventionally, flow sensors have been using the method of resistance measurement. The method senses the change in electrical resistance of a filament because of a change in temperature caused by the flow of material across the filament. Balancing the resistance of the filament is a time-consuming method, which forms the major disadvantage of this method and makes it expensive.

In contrast, the MEMS flow sensor utilizes a thermopile, an element that converts thermal energy into electrical energy. This technology offers several advantages not seen earlier. For instance, MEMS technology offers cheaper operation, only a few adjustments, high sensitivity, and low power consumption.

This advanced sensor can even sense the direction of flow. The chip has two sets of thermopiles located on either side of a tiny heater element. The thermopiles measure the deviations in heat symmetry that the gas flow causes. The chip senses the direction of flow based on a positive or a negative deviation. A thin layer of insulating film covers the sensor chip and protects it from being exposed to the gas.

In the absence of flow, temperature distribution remains uniform around the heater and there is no differential voltage between the two thermopiles. With even the smallest flow, the heat symmetry collapses, as the thermopile on the side of the heater facing the flow shows a lower temperature, while the thermopile on the other side is warmer. This temperature difference causes a differential voltage to appear between the two thermopiles. This voltage is proportional to the mass flow rate.

The superb characteristic of the sensing chip comes from an unusual shape created by a unique etching technology. Compared to the conventional silicon etching, this unique etching technology creates a larger sensing area in the same volume. This results in a cavity design enabling heating with greater efficiency while keeping the power consumption low. Additionally, the cross-point of temperature characteristic can be factory adjusted, which results in high output stability even when the ambient temperature fluctuates.

Within the actual sensor, a set of screens in the sensor inlet produces a uniform, laminar flow through the sensor offering optimal mass flow readings. An orifice in the outlet side of the sensor buffers against pulsing flows.

Which Raspberry Pi Should I Use?

Which Raspberry Pi or RBPi you will use is getting more and more difficult to answer as the family keeps growing. It was simple and straightforward when the RBPi first launched – there was only one model. Since then, with four major models to choose from, things are more complicated. However, this versatile beast comes in different specifications and you should select the one most fitting your requirements. Among the models available, here is a summary to help you decide:

RBPi Zero

This is the latest addition to the family. Although it is ultra-cheap, the RBPi Zero is definitely a fully functional single board computer. Compared to the first model of family, the processor used in the RBPi Zero is more than 40% faster. However, purchasing this variant compels you to make major compromises.

To start with, you will need adapters to use the mini HDMI and micro USB ports on the device. As there is no on-board Ethernet port, you need to use the single USB port. Although you can expand its functionality by adding a powered USB hub, the additions begin to detract from the major selling point of the Zero – its tiny footprint.

If the application does not require a fair amount of connectivity, is low-powered and for single-use, you may consider using the RBPi Zero.

RBPi Model A+

Although a full-sized version, this model also lacks the Ethernet port and has only one USB port. Moreover, it has only 256GB RAM that goes with the 700MHz processor. The price and lack of power makes it difficult to recommend the RBPi Model A+ for any application other than for specific ones.

RBPi Model B+

If performance is not a criteria and price is the only consideration, then the RBPi Model B is hard to beat. The model offers good connectivity as it has on-board Ethernet, four USB ports and a full sized HDMI connector. That makes the RBPi Model B+ more versatile than either the Model A+ or the RBPi Zero.

You can use it for any project that requires good connectivity, less than top-notch performance, and low power.

RBPi Model 2

This is the top-of-the-line model in the family and a surprisingly capable beast. With an updated chipset, a quad-core processor and 1GB RAM, the RBPi Model 2 makes a major difference in the large variety of Single Board Computers available in the market.

You can use the RBPi Model 2 as a media server for your network or use it for tasks of more intensive nature such as running a home surveillance system or playing games. It also allows you to explore platforms other than Linux – you can run the IoT version of Windows 10.

Even though the total power consumed by the RBPi Model 2 is below 1W, it uses significantly more power as compared to its predecessors. For example, RBPi Model 2 consumes more than 33% power drawn in by the RBPi Model B+ and five times more power than what the RBPi Zero consumes. Use the RBPi Model 2 for anything where you need good performance.

Check our other guides for information on Model 3.